Recently, due to rapid development in the photographic technology, development and realization of silver halide light-sensitive photographic materials which have higher sensitivity and image quality and which are adaptable to rapid process has strongly been demanded.
For instance, in the field of radiology and X-ray light-sensitive photographic materials for medical use, with the increase in the chances of medical examination, items of medical inspections and the number of chances of shooting pictures have also increased. And, because of necessity for doctors to know the results of inspections as soon as possible, improved rapid-processability of the light-sensitive photographic materials becomes a stronger demand than ever before.
Particularly, pictures of arteriography or those taken during an operation require images of higher image quality as quickly as possible.
To answer the demand mentioned above, a light-sensitive material which comprises tabular-shape silver halide grains has recently been proposed.
The tabular-shaped silver halide grain, because of its relatively large specific surface area, can adsorb a large quantity of a spectral sensitizing dye. Therefore, in addition to improvements in spectral sensitization, the photographic material comprising tabular grains has an advantage that not only high sensitivity and high image sharpness may easily be obtained but also crossover light through the light-sensitive material can be reduced.
However, in general, tabular grains with a large diameter-thickness ratio have a disadvantage that they are weak against external force because of their shape. Therefore, for instance, when the light-sensitive material is folded while it is handled, or when mechanical stress is added to it during transportation, bends tend to be caused. And as the result thereof serious defects such a blackening like a streak, fogging by the pressure and desensitization are likely to take place, which can be a serious problem in the case of photographic materials for diagnostic use.
Two methods have been proposed as a means for preventing sensitivity from the pressure.
One method is physically to relax the stress acted on the silver halide grain when an external pressure is applied to photographic material.
Another method is to decrease pressure sensitivity of the silver halide crystal itself.
As the approach of the former, for example, there have been disclosed methods for covering the crystal surface by using gelatin, a hydrophilic polymer or a latex as a binder of an emulsion layer, or incorporating a gelatin plasticizer or a substance adsorbable to silver halide grains.
However, these methods result in a slow down of the speed of development and drying. This is against the current demand and is undesirable.
As the latter approach from silver halide crystal, for example, a method of providing a high silver iodide-containing layer inside the tabular grain as disclosed in Japanese Patent O.P.I. Publication No. 59-99433 (1984) for the purpose of improving pressure resistance, or a method disclosed in Japanese Patent O.P.I. Publication No. 61-14636 (1986), etc., in which pressure resistance may be improved by raising the silver iodide content in the central portion of the tabular grains more than that of the outer portion, etc. are known.
However, according to the latter method, although some improvement in the pressure resistance may be recognized, a remarkable deterioration in developability is induced, and, for example, when the average silver iodide content of the entire grains is lowered, development speed tends to exceed and, as a result, a problem of deterioration in the graininess arises.
Since deterioration of the graininess in the photographic light-sensitive material, especially in the x-ray images, can lead to a wrong diagnosis, a method which has a strong effect on the developability of the photographic material is undesirable and a new countermeasure against this has been demanded.